The primary aim of this project is to test the specificity of the association between abnormal levels of arousal during REM sleep and mood dysregulation in a cohort of patients with major depression and matched normal controls. Our interest in this association derives from a theoretical perspective which posits that REM sleep serves a mood regulatory function and that arousal during REM sleep may be related to a dysfunction in this system. In a preliminary study of arousal during sleep in subjects with major depression, we found that motor activity during REM sleep, as measured from the corrugator muscle, positively correlated with a measure of depressive severity that largely reflects that cognitive/affective components of depression. In the proposed investigation, we will evaluate several skeletal muscle groups in depressed and non-depressed subjects across three behavioral states (waking, NREM sleep and REM sleep) to determine the specificity of this phenomenon for depression, particular muscle groups and for REM sleep.. We will also evaluate several mood states and other measures of physiological arousal in order to determine whether the REM sleep arousal depression interaction is specific to the corrugator measure and to measures of depression as opposed to general measures of dysphoria or negative affect. Future work is proposed to evaluate the central mechanisms of REM-related arousal and their association with the development, clinical course and recurrence of depression. The proposed line of study promises to provide a functional explanation for why sleep abnormalities put the individual at risk for development of depression.